1. Field of the Invention
The present invention relates to die-bonding equipment and methods for detecting whether an adhesive such as Ag-epoxy is properly dotted on a die pad of a lead frame or a substrate, enabling timely replacement of adhesive tubes and preventing poor bonding of a semiconductor chip to the die pad.
2. Description of the Related Art
Generally, an assembly process of semiconductor packages includes: dicing of a wafer including a number of semiconductor chips into individual semiconductor chips; bonding of each semiconductor chip on a die pad of a lead frame using an adhesive; wire-bonding to connect the bonding pads of the semiconductor chip to inner leads of the lead frame; encapsulation of the semiconductor chip, the wire and the inner leads with a molding compound to protect the semiconductor chip from the external environment; singulation of each individual package and forming outer leads of the lead frame; and marking of a trademark and a product serial number on the package.
In the die-bonding process, the lead frame is placed at a predetermined position by a transferring unit, and an adhesive is dotted on the die pad of the lead frame by a dispenser in the die-bonding equipment. Then, a bonding-head picks up a semiconductor chip and attaches the backside of the semiconductor chip to the die pad. The final step of the die-bonding process is curing of the adhesive.
Ag-epoxy adhesive is commonly used as an adhesive between a die pad and a semiconductor chip. In the die-bonding equipment, Ag-epoxy adhesive contained in a tube is loaded in a dispenser. When the tube is empty or nearly empty, an operator of the apparatus replaces the tube with a new tube.
To select when to replace the tube, the operator loads a new adhesive tube, and sets a controlling unit with an expected number of dotting operation from the tube. When operating, the equipment counts actual adhesive dotting, and when the count is the same as the set number, the control unit alerts operator to inform the operator that the presently used tube is running out of the adhesive and needs to be replaced with a new one. Thus, the operator replaces the adhesive tube according to the number of dottings, not according to the state of adhesive dotting on the die pad. Generally, the operator changes the expected number of dottings according to the size of semiconductor chips because larger chips need more adhesive for die bonding. However, the expected number set by the operator can be incorrect due to a miscalculation of the chip size and adhesive use at an expected rate, or human error in setting the expected number. The set number being incorrect can result in waste of adhesive if tubes are changed too often or improper bonding if tubes are changed too infrequently.